A: Concept: A digital signature (also known as a public key digital signature) is a number string, which can only be generated by the sender of the information and cannot be forged by others. This number string is also an effective proof of the authenticity of the information sent by the information sender. It is a method to authenticate digital information, which is similar to the ordinary physical signature written on paper, but it is realized by using the technology in the field of public key encryption. A set of digital signatures usually defines two complementary operations, one for signing and the other for verification. Digital signature is the application of asymmetric key encryption technology and digital digest technology.

Basic principle: the integrity of digital signature documents is easy to verify (no need for sewing stamps, sewing signatures or handwriting experts), and digital signatures are undeniable. Simply put, the so-called digital signature is some data attached to the data unit, or the cryptographic transformation of the data unit. This kind of data or transformation allows the receiver of the data unit to confirm the source and integrity of the data unit, and protects the data from being forged by people (such as the receiver). This is a method of signing an electronic message, and the signed message can be transmitted in a communication network. Digital signature can be obtained based on both public key cryptosystem and private key cryptosystem, mainly digital signature based on public key cryptosystem. Include general digital signature and special digital signature. Common digital signature algorithms include RSA, ElGamal, Fiat-Shamir, Guillou-Quisqour, Schnorr, Ong-Schnorr-Shamir, Des/DSA, elliptic curve digital signature algorithm and finite automaton digital signature algorithm. Special digital signatures include blind signature, proxy signature, group signature, undeniable signature, fair blind signature, threshold signature, signature with message recovery function and so on. It is closely related to the specific application environment. Obviously, the application of digital signature involves legal issues, and the federal government of the United States has formulated its own digital signature standard (DSS) based on the discrete logarithm problem over a finite field.